(425f) Plant-Wide Modelling and Techno-Economic Analysis of Hydrogen Production Using Coal Refuse with and without Biomass

Coal has long been a primary fuel for power generation, leading to significant piles of refuse all over the world from various coal production stages, such as mining, washing, and gasification. These piles are hazardous to the environment and pose threats of autoignition of carbonaceous fuels and exothermic pyrite oxidation, which emit greenhouse gases (GHGs) like CO₂ and SO_x that cause air pollution. In states like Pennsylvania, where 840 coal refuse piles were documented in 2016, 52 are actively burning. Coal refuse also occupies valuable land, sometimes near waterways, potentially leading to acid mine drainage due to acidic minerals like sulfates, phosphates, silica (SiO₂), and alumina (Al₂O₃). Accumulated coal refuse piles can easily collapse, which can be hazardous to neighboring communities. Mitigating these challenges has called for various methods of coal refuse utilization. One possible method that we investigate in this work is hydrogen (H₂) production through co-gasification of biomass and coal refuse. Detailed plant-wide process modeling is undertaken by considering various alternative routes when coal refuse is utilized with and without biomass for H₂ production. Economic models are developed, and techno-economic (TEA) analyses are undertaken. Overall, this work seeks to make several contributions. This work investigates, for the first time to the best of our knowledge, use of coal refuse, by itself, and as a blend with biomass, as a feedstock for H₂ production This work also proposes a plant-wide process for the proposed process, where one of the key steps that is integrated is a column flotation process in the pre-treatment step of the coal refuse for deashing. In addition, the techno-economic analysis and sensitivity studies are conducted that indicate the tradeoff between the economic and environmental performance of various processing steps and design and operating variables such as the degree of ash separation in the ash flotation step, impact of biomass:coal ratio, etc.

Coal and biomass co-gasification offers synergistic advantages from both feedstocks; coal provides a high carbon source with its C/O₂ ratio, while biomass contributes additional oxygen during gasification with its low C/O₂ ratio. In addition, biomass gasifies at lower temperatures (800°C to 950°C) compared to coal (950°C to 1100°C)[1], allowing co-gasification to decrease activation energy requirements and start gasification at a lower temperature because of the high volatility of biomass. Since coal refuse has a high ash content, sometimes reaching up to 60%[2], it must undergo deashing not only for being economically and energetically favorable, but also for preventing the combustion of acidic and alkaline components that could generate GHG emissions. Numerous commercial deashing techniques exist, including jigging, hydrocyclones, and flotation techniques. Column flotation is chosen in this study because it is economical, highly efficient for ash separation, and easy to separate off both fines and gobs[3]. In this study, four process models are generated using Aspen Plus with different coal refuse-to-biomass ratios: 1:0, 4:1 (base case), 3:1, and 0:1. All models undergo co-gasification using a bubbling fluidized bed reactor[4]. For all models, the H₂ production rate remains the same for either 50 MWe distributed power production using a simple cycle process or 500 MWe centralized power production through a combined cycle process[5]. The pressure swing adsorption (PSA) unit is modeled and designed to generate H₂ with a 99.99% purity, which is compressed to various pressure levels depending on its target utilization.

The process model information from Aspen Plus V14^® is transferred to Aspen Process Economic Analyzer (APEA) for TEA. Uncertainty analysis is undertaken to consider uncertainties in various technical and economic parameters such as gasifier costs, and biomass costs to obtain an uncertainty envelope for achieving the $2/kg hydrogen target. Sensitivity to plant scale is also undertaken.

References

[1] C. Higman and M. van der Burgt, Gasification, 2nd ed. Amsterdam ; Boston: Gulf Professional Pub./Elsevier Science, 2008.

[2] W. H. Buttermore, E. J. Simcoe, and M. A. Maloy, “Characterization of Coal Refuse (No. FE-1218-T3; 159).” West Virginia Univ., Morgantown (United States). Coal Research Bureau, 1979.

[3] N. Vasumathi, T. Vijaya-Kumar, K. Prasad, S. Subba-Rao, S. Prabhakar, and G. Bhaskar-Raju, “Fine Coal Beneficiation by Pilot Column Flotation,” J Min & Metal A Mining, vol. 54, no. 1, pp. 25–33, 2018, doi: 10.5937/JMMA1801025V.

[4] P. Spath, A. Aden, T. Eggeman, M. Ringer, B. Wallace, and J. Jechura, “Biomass to Hydrogen Production Detailed Design and Economics Utilizing the Battelle Columbus Laboratory Indirectly-Heated Gasifier,” NREL/TP-510-37408, 15016221, May 2005. doi: 10.2172/15016221.

[5] T. Wei, Z. Hu, X. Tang, and H. Zhang, “Performance Evaluation of a Hydrogen-Fired Combined Cycle with Water Recovery,” Case Studies in Thermal Engineering, vol. 44, p. 102863, Apr. 2023, doi: 10.1016/j.csite.2023.102863.